docs: def get_symbol(units) -> str:
      """Get default symbol type.
  
      Parameters
      ----------
      units_str : string
          Units.
  
      Returns
      -------
      string
          LaTeX formatted symbol.
      """
      if kind(units) == "energy":
          d = {}
          d["nm"] = r"\lambda"
          d["wn"] = r"\bar\nu"
          d["eV"] = r"\hslash\omega"
          d["Hz"] = r"f"
          d["THz"] = r"f"
          d["GHz"] = r"f"
          return d.get(units, "E")
      elif kind(units) == "delay":
          return r"\tau"
      elif kind(units) == "fluence":
          return r"\mathcal{F}"
      elif kind(units) == "pulse_width":
          return r"\sigma"
      elif kind(units) == "temperature":
          return r"T"
      else:
          return kind(units)